// Copyright 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "base/message_loop/incoming_task_queue.h"

#include <limits>

#include "base/location.h"
#include "base/message_loop/message_loop.h"
#include "base/synchronization/waitable_event.h"
#include "base/time/time.h"
#include "build/build_config.h"

namespace base {
namespace internal {

    namespace {

#if !defined(NDEBUG) || defined(DCHECK_ALWAYS_ON)
        // Delays larger than this are often bogus, and a warning should be emitted in
        // debug builds to warn developers.  http://crbug.com/450045
        const int kTaskDelayWarningThresholdInSeconds = 14 * 24 * 60 * 60; // 14 days.
#endif

        // Returns true if MessagePump::ScheduleWork() must be called one
        // time for every task that is added to the MessageLoop incoming queue.
        bool AlwaysNotifyPump(MessageLoop::Type type)
        {
#if defined(OS_ANDROID)
            // The Android UI message loop needs to get notified each time a task is
            // added
            // to the incoming queue.
            return type == MessageLoop::TYPE_UI || type == MessageLoop::TYPE_JAVA;
#else
            return false;
#endif
        }

        TimeTicks CalculateDelayedRuntime(TimeDelta delay)
        {
            TimeTicks delayed_run_time;
            if (delay > TimeDelta())
                delayed_run_time = TimeTicks::Now() + delay;
            else
                DCHECK_EQ(delay.InMilliseconds(), 0); // << "delay should not be negative";
            return delayed_run_time;
        }

    } // namespace

    IncomingTaskQueue::IncomingTaskQueue(MessageLoop* message_loop)
        : high_res_task_count_(0)
        , message_loop_(message_loop)
        , next_sequence_num_(0)
        , message_loop_scheduled_(false)
        , always_schedule_work_(AlwaysNotifyPump(message_loop_->type()))
        , is_ready_for_scheduling_(false)
    {
    }

    bool IncomingTaskQueue::AddToIncomingQueue(
        const tracked_objects::Location& from_here,
        const Closure& task,
        TimeDelta delay,
        bool nestable)
    {
        DLOG_IF(WARNING,
            delay.InSeconds() > kTaskDelayWarningThresholdInSeconds)
            << "Requesting super-long task delay period of " << delay.InSeconds()
            << " seconds from here: " << from_here.ToString();

        PendingTask pending_task(
            from_here, task, CalculateDelayedRuntime(delay), nestable);
#if defined(OS_WIN)
        // We consider the task needs a high resolution timer if the delay is
        // more than 0 and less than 32ms. This caps the relative error to
        // less than 50% : a 33ms wait can wake at 48ms since the default
        // resolution on Windows is between 10 and 15ms.
        if (delay > TimeDelta() && delay.InMilliseconds() < (2 * Time::kMinLowResolutionThresholdMs)) {
            pending_task.is_high_res = true;
        }
#endif
        return PostPendingTask(&pending_task);
    }

    bool IncomingTaskQueue::HasHighResolutionTasks()
    {
        AutoLock lock(incoming_queue_lock_);
        return high_res_task_count_ > 0;
    }

    bool IncomingTaskQueue::IsIdleForTesting()
    {
        AutoLock lock(incoming_queue_lock_);
        return incoming_queue_.empty();
    }

    int IncomingTaskQueue::ReloadWorkQueue(TaskQueue* work_queue)
    {
        // Make sure no tasks are lost.
        DCHECK(work_queue->empty());

        // Acquire all we can from the inter-thread queue with one lock acquisition.
        AutoLock lock(incoming_queue_lock_);
        if (incoming_queue_.empty()) {
            // If the loop attempts to reload but there are no tasks in the incoming
            // queue, that means it will go to sleep waiting for more work. If the
            // incoming queue becomes nonempty we need to schedule it again.
            message_loop_scheduled_ = false;
        } else {
            incoming_queue_.swap(*work_queue);
        }
        // Reset the count of high resolution tasks since our queue is now empty.
        int high_res_tasks = high_res_task_count_;
        high_res_task_count_ = 0;
        return high_res_tasks;
    }

    void IncomingTaskQueue::WillDestroyCurrentMessageLoop()
    {
        base::subtle::AutoWriteLock lock(message_loop_lock_);
        message_loop_ = NULL;
    }

    void IncomingTaskQueue::StartScheduling()
    {
        bool schedule_work;
        {
            AutoLock lock(incoming_queue_lock_);
            DCHECK(!is_ready_for_scheduling_);
            DCHECK(!message_loop_scheduled_);
            is_ready_for_scheduling_ = true;
            schedule_work = !incoming_queue_.empty();
        }
        if (schedule_work) {
            DCHECK(message_loop_);
            // Don't need to lock |message_loop_lock_| here because this function is
            // called by MessageLoop on its thread.
            message_loop_->ScheduleWork();
        }
    }

    IncomingTaskQueue::~IncomingTaskQueue()
    {
        // Verify that WillDestroyCurrentMessageLoop() has been called.
        DCHECK(!message_loop_);
    }

    bool IncomingTaskQueue::PostPendingTask(PendingTask* pending_task)
    {
        // Warning: Don't try to short-circuit, and handle this thread's tasks more
        // directly, as it could starve handling of foreign threads.  Put every task
        // into this queue.

        // Ensures |message_loop_| isn't destroyed while running.
        base::subtle::AutoReadLock hold_message_loop(message_loop_lock_);

        if (!message_loop_) {
            pending_task->task.Reset();
            return false;
        }

        bool schedule_work = false;
        {
            AutoLock hold(incoming_queue_lock_);

#if defined(OS_WIN)
            if (pending_task->is_high_res)
                ++high_res_task_count_;
#endif

            // Initialize the sequence number. The sequence number is used for delayed
            // tasks (to facilitate FIFO sorting when two tasks have the same
            // delayed_run_time value) and for identifying the task in about:tracing.
            pending_task->sequence_num = next_sequence_num_++;

            message_loop_->task_annotator()->DidQueueTask("MessageLoop::PostTask",
                *pending_task);

            bool was_empty = incoming_queue_.empty();
            incoming_queue_.push(std::move(*pending_task));

            if (is_ready_for_scheduling_ && (always_schedule_work_ || (!message_loop_scheduled_ && was_empty))) {
                schedule_work = true;
                // After we've scheduled the message loop, we do not need to do so again
                // until we know it has processed all of the work in our queue and is
                // waiting for more work again. The message loop will always attempt to
                // reload from the incoming queue before waiting again so we clear this
                // flag in ReloadWorkQueue().
                message_loop_scheduled_ = true;
            }
        }

        // Wake up the message loop and schedule work. This is done outside
        // |incoming_queue_lock_| because signaling the message loop may cause this
        // thread to be switched. If |incoming_queue_lock_| is held, any other thread
        // that wants to post a task will be blocked until this thread switches back
        // in and releases |incoming_queue_lock_|.
        if (schedule_work)
            message_loop_->ScheduleWork();

        return true;
    }

} // namespace internal
} // namespace base
